Proposition 18 (C.f. Proposition 3.4 on p. 11 of [1]}) 

Let \(B > 0\) , \(b \in (0,\tfrac{1}{4B}]\)  and \(\theta \in \mathbb {R}\) . Then, the following are equivalent for \(f,g \in \mathcal {F}_{-\theta } L^4([-B,B])\) :
